An Introduction to the Brain and Cranial Nerves The Adult Human Brain Contains almost 97% of the...
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Transcript of An Introduction to the Brain and Cranial Nerves The Adult Human Brain Contains almost 97% of the...
An Introduction to the Brain and Cranial Nerves
The Adult Human Brain
Contains almost 97% of the body’s neural
tissue
Average weight about 1.4 kg (3 lb)
About 400 g at birth
Adult range = 1100-1700 g
Reached by about 18 yoa
Decline in weight starts at about age 50
The Brain
Eight Major Regions of the Brain Cortex (Cerebrum)
Limbic System
Thalamus
Hypothalamus
Cerebellum
Midbrain (Mesencephalon)
Pons
Medulla oblongata
Diencephalon
Brainstem
The Brain
Fig 14-1
Brain Protection and Support
Physical protection
Bones of the cranium
Cranial meninges
Cerebrospinal fluid
Biochemical isolation
Blood–brain barrier
Brain Protection and Support
The Cranial Meninges
Have three layers:
Dura mater (“tough mother” – attached to inner surface of skull)
Arachnoid mater (web-like matrix)
– Space between arachnoid and pia is filled with CSF
Pia mater (“tender mother” – attached to the brain)
Are continuous with spinal meninges
Protect the brain from cranial trauma
Brain Protection and Support
The Cranial Meninges Dura mater
Inner fibrous layer (meningeal layer)
Outer fibrous layer (endosteal layer) fused to periosteum
Venous sinuses form between the two layers (dural sinuses)
Arachnoid mater Covers brain
Contacts epithelial layer of dura mater
Subarachnoid space: between arachnoid mater and pia mater
Pia mater Covered by many blood vessels and attached to brain
surface by astrocytes
Brain Protection and Support
Fig 14-3
Brain Protection and Support
Dural Folds
Folded inner layer of dura mater
Extend into cranial cavity
Stabilize and support brain
Contain collecting veins (dural sinuses), where
cerebral veins will empty
Falx cerebri, tentorium cerebelli, and falx cerebelli
Brain Protection and Support
Dural Folds Falx cerebri
Projects into the longitudinal fissure between the cerebral
hemispheres
Contains superior sagittal sinus and inferior sagittal sinus
Tentorium cerebelli Separates cerebellum and cerebrum
Contains transverse sinus
Falx cerebelli Divides cerebellar hemispheres below the tentorium cerebelli
Brain Protection and Support
Fig 14-3
The Ventricular System
Fig 14-2
Cerebrospinal Fluid
Cerebrospinal Fluid (CSF)
Surrounds all exposed surfaces of CNS
Interchanges with interstitial fluid of brain
Functions of CSF
Cushions delicate neural structures
Supports brain
Transports nutrients, chemical messengers, and
waste products
Cerebrospinal Fluid Cerebrospinal Fluid (CSF)
Choroid plexus
Specialized ependymal cells and capillaries:
– secrete CSF into ventricles
– remove waste products from CSF
– adjust composition of CSF
Produces about 500 mL of CSF/day
– About 130 mLs within and around the brain and spinal cord
at any given time
– About 20 mLs within the ventricles; Remainder in
subarachnoid space
Cerebrospinal Fluid
Cerebrospinal Fluid (CSF)
CSF circulates
From choroid plexus
Through ventricles
To central canal of spinal cord
Into subarachnoid space around the brain, spinal
cord, and cauda equina
Cerebrospinal Fluid
Cerebrospinal Fluid (CSF)
CSF in subarachnoid space
Arachnoid villi:
– extensions of subarachnoid space
– extend through dura mater to superior sagittal sinus
Arachnoid granulations:
– large clusters of villi
– absorb CSF into venous circulation
Cerebrospinal Fluid
Fig 14-4
Hydrocephalus or “water on the brain” may result from _____.
A.deficient production of CSFB.excessive production of CSFC.blockage of circulation of CSFD.excessive water intakeE.B or C
Arterial Blood Supply
Blood Supply to the Brain
Supplies nutrients and oxygen to brain
Delivered by internal carotid arteries and
vertebral arteries
Removed from dural sinuses by internal
jugular veins
Arterial Blood Supply
Fig 21-22
Arterial Blood Supply
Fig 21-23
Venous Drainage
Fig 21-28
Venous Drainage
Fig 21-28
Cerebrovascular Disease
Cerebrovascular Disease
Disorders interfere with blood circulation to brain
Stroke or cerebrovascular accident (CVA)
Shuts off blood to portion of brain
Neurons die
The brain requires a substantial blood supply. The vessels that deliver blood to the brain are the _____.
A.internal carotid arteriesB.vertebral arteriesC.jugular veinsD.A and B onlyE.A, B, and C
Blood-Brain Barrier
Blood–Brain Barrier
Isolates CNS neural tissue from general circulation
Formed by network of tight junctions between
endothelial cells of CNS capillaries
Lipid-soluble compounds (O2, CO2), steroids, and
prostaglandins can diffuse into interstitial fluid of brain
and spinal cord
Astrocytes control blood–brain barrier by releasing
chemicals that control permeability of endothelium
Blood-CSF Barrier
Blood–CSF Barrier
Formed by special ependymal cells
Surround capillaries of choroid plexus
Limits movement of compounds transferred
Allows chemical composition of blood and CSF to
differ
Blood Brain Barrier
Four Breaks in the BBB Portions of hypothalamus
Secrete hypothalamic hormones
Posterior lobe of pituitary gland Secretes hormones ADH and oxytocin
Pineal glands Pineal secretions
Choroid plexus Where special ependymal cells maintain blood–
CSF barrier
Blood Brain Barrier
Meninges stabilize brain in cranial cavity
Cerebrospinal fluid protects against sudden
movement
CSF provides nutrients and removes wastes
Blood–brain barrier and blood–CSF barrier
Selectively isolate brain from chemicals in blood that
might disrupt neural function
The Brain
Fig 14-1
The Brain Stem
The Brain Stem
Processes information
between
Spinal cord and
cerebrum or cerebellum
Includes
Mesencephalon
(midbrain)
Pons
Medulla oblongata
The Medulla Oblongata
The Brain Stem
Medulla oblongata
Connects brain to spinal
cord
Relays information
Regulates autonomic
functions:
– heart rate, blood pressure,
respiration and digestion
The Medulla Oblongata
The Medulla Oblongata
Allows brain and spinal cord to communicate
Coordinates complex autonomic reflexes
Controls visceral functions
Nuclei in the Medulla
Autonomic nuclei: control visceral activities
Sensory and motor nuclei: of cranial nerves
Relay stations: along sensory and motor pathways
The Medulla Oblongata
Autonomic Nuclei of the Medulla Oblongata Reticular formation
Gray matter with embedded nuclei
Regulates autonomic functions
Reflex centers Control peripheral systems:
– cardiovascular centers:
» cardiac center
» control blood flow through peripheral tissues
– respiratory rhythmicity centers
sets pace for respiratory movements
The Medulla Oblongata
Relay Stations of the Medulla Oblongata
Nucleus gracilis and nucleus cuneatus
Pass somatic sensory information to thalamus
Solitary nucleus
Receives visceral sensory information
Olivary nuclei (olives)
Relay information about somatic motor commands
The Medulla Oblongata
Fig 14-6
The Medulla Oblongata
Fig 14-6
The medulla oblongata regulates _____.
A.blood pressureB.food intakeC.respirationD.both A and BE.both A and C
The Pons
The Pons
Connects cerebellum to brain stem
Links to mesencephalon, diencephalon, cerebrum
and spinal cord
Is involved in somatic and visceral motor
control
The Pons
Fig 14-6
The Pons
The Pons Nuclei involved with respiration
Apneustic center and pneumotaxic center: – modify respiratory rhythmicity center activity
Nuclei and tracts Process and relay information to and from
cerebellum Ascending, descending, and transverse tracts:
– transverse fibers (axons):
» link nuclei of pons with opposite cerebellar hemisphere
The Pons
Fig 14-6
The Pons contains:
A.sensory and motor nuclei for four cranial nerves.B.nuclei concerned with the control of respiration.C.tracts that link the cerebellum with the brain stem.D.All of the above
The Mesencephalon
The Brain Stem
Mesencephalon
Also called midbrain
Processes sight, sound, and associated reflexes
Maintains consciousness
The Mesencephalon
Structures of the Mesencephalon
Tectum
Two pairs of sensory nuclei (corpora quadrigemina):
– superior colliculus (visual)
– inferior colliculus (auditory)
Tegmentum
Red nucleus (many blood vessels)
Substantia nigra (pigmented gray matter)
The Mesencephalon
Fig 14-8
The Mesencephalon
Structures of the
Mesencephalon
Cerebral peduncles
Nerve fiber bundles on
ventrolateral surfaces
Contain:
– descending fibers to cerebellum
– motor command fibers
Damage to the superior colliculi would interfere with the reflex ability to _____.
A.express rageB.voluntarily move the armC.react to a bright lightD.react to loud noisesE.maintain proper posture
The Cerebellum
Cerebellum
Second largest part of brain
Coordinates repetitive body
movements
Two hemispheres
Covered with cerebellar
cortex
The Cerebellum
Functions of the Cerebellum
Adjusts postural muscles
Fine-tunes conscious and subconscious
movements
The Cerebellum
Structures of the Cerebellum Folia
Surface of cerebellum Highly folded neural cortex
Anterior and posterior lobes Separated by primary fissure
Cerebellar hemispheres: Separated at midline by vermis
Vermis Narrow band of cortex
Flocculonodular lobe Below fourth ventricle
The Cerebellum
Structures of the Cerebellum
Purkinje cells
Large, branched cells
Found in cerebellar cortex
Receive input from up to 200,000 synapses
Arbor vitae
Highly branched, internal white matter of cerebellum
Cerebellar nuclei: embedded in arbor vitae:
– relay information to Purkinje cells
The Cerebellum
Structures of the Cerebellum
The peduncles
Tracts link cerebellum with brain stem, cerebrum, and spinal
cord:
– superior cerebellar peduncles
– middle cerebellar peduncles (links cerebellum with pons)
– inferior cerebellar peduncles
The Cerebellum
Disorders of the Cerebellum
Ataxia
Damage from trauma or stroke
Intoxication (temporary impairment)
Disturbs muscle coordination
The Cerebellum
Fig 14-7
The Cerebellum
Fig 14-7
Overseeing the postural muscles of the body and making rapid adjustments to maintain balance and equilibrium are functions of the _____.
A.cerebrumB.mesencephalonC.cerebellumD.ponsE.medulla oblongata
The Diencephalon
Diencephalon
Located under cerebrum
and cerebellum
Links cerebrum with
brain stem
Two divisions
Thalamus
Hypothalamus
The Diencephalon
Diencephalon Thalamus
Relays and processes sensory information
Hypothalamus Hormone production Emotion Autonomic function
Pituitary gland Major endocrine gland Connected to hypothalamus Via infundibulum (stalk) Interfaces nervous and
endocrine systems
The Diencephalon
The Thalamus Filters ascending sensory information for primary
sensory cortex
Relays information between basal nuclei and cerebral
cortex
The third ventricle Separates left thalamus and right thalamus
Interthalamic adhesion (or intermediate mass):
– projection of gray matter
– extends into ventricle from each side
The Diencephalon
The Thalamus
Thalamic nuclei
Are rounded masses that form thalamus
Relay sensory information to basal nuclei and
cerebral cortex
The Diencephalon
Five Groups of Thalamic Nuclei
Anterior group
Anterior nuclei
Part of limbic system (emotions)
Medial group
Provides awareness of emotional states
Ventral group
Relays sensory information from basal ganglia and
cerebellum
The Diencephalon
Five Groups of Thalamic Nuclei
Posterior group
Pulvinar nucleus (sensory)
Lateral geniculate nucleus (visual)
Medial geniculate nucleus (auditory)
Lateral group
Affects emotional states
Integrates sensory information
The Diencephalon
Fig 14-9
The Diencephalon
The Hypothalamus Mamillary bodies
Located in posterior hypothalamus
Process olfactory and other sensory information
Control reflex eating movements
Infundibulum A narrow stalk
Connects hypothalamus to pituitary gland
Tuberal area Located between the infundibulum and mamillary bodies
Helps control pituitary gland function
The Diencephalon
Fig 14-10
The Diencephalon
Fig 14-10
The Diencephalon
Eight Functions of the Hypothalamus
Provides subconscious control of skeletal muscle
Controls autonomic function
Coordinates activities of nervous and endocrine
systems
Secretes hormones
Antidiuretic hormone (ADH) by supraoptic nucleus
Oxytocin (OT; OXT) by paraventricular nucleus
The Diencephalon
Eight Functions of the Hypothalamus
Produces emotions and behavioral drives
The feeding center (hunger)
The thirst center (thirst)
Coordinates voluntary and autonomic functions
Regulates body temperature
Preoptic area of hypothalamus
Controls circadian rhythms (day–night cycles)
Suprachiasmatic nucleus
JoJo begins to experience mood swings and disturbed thirst and hunger. Imaging studies indicate that a brain turmor is the likely cause of these disorders. In what part of the brain is the tumor most likely located?
A.Prefrontal cortexB.Postcentral gyrusC.Basal nucleiD.HypothalamusE.Reticular formation
The Limbic System
The Limbic System
Is a functional grouping that
Establishes emotional states
Links conscious functions of cerebral cortex with
autonomic functions of brain stem
Facilitates memory storage and retrieval
The Limbic System
Components of the Limbic System Amygdaloid body
Acts as interface between the limbic system, the
cerebrum, and various sensory systems
Limbic lobe of cerebral hemisphere Cingulate gyrus
Dentate gyrus
Parahippocampal gyrus
Hippocampus – storage and recall of long-term
memories
The Limbic System
Components of the Limbic System Fornix
Tract of white matter Connects hippocampus with hypothalamus
Anterior nucleus of the thalamus Relays information from mamillary body to
cingulate gyrus
Reticular formation Stimulation or inhibition affects emotions (rage,
fear, pain, sexual arousal, pleasure)
The Limbic System
Fig 14-11
The Limbic System
Fig 14-11
Which of the following is not a function of the limbic system?
A.Contains cerebral and diencephalic componentsB.Functions in maintaining homeostasis in cold weatherC.Located between the border of the cerebrum and diencephalonD.Links conscious functions of the cerebral cortex with unconscious functions of the brain stemE.Functions in emotions, learning, and memory
The Brain
Cerebrum (Cortex)
Largest part of brain
Controls higher mental
functions
Divided into left and right
cerebral hemispheres
The Brain
Cerebrum
Neural cortex
Also called cerebral cortex
Folded surface increases surface area
Elevated ridges (gyri)
Shallow depressions (sulci)
Deep grooves (fissures)
The Cerebrum
The Cerebrum
Is the largest part of the brain
Controls all conscious thoughts and
intellectual functions
Processes somatic sensory and motor
information
The Cerebrum
Gray matter
In cerebral cortex and
basal nuclei
White matter
Deep to basal cortex
Around basal nuclei
The Cerebrum
Structures of the Cerebrum Gyri of neural cortex
Increase surface area (number of cortical neurons)
Insula (island) of cortex Lies medial to lateral sulcus
Longitudinal fissure Separates cerebral hemispheres
Lobes Divisions of hemispheres named after overlying
skull bones
The Cerebrum
Structures of the Cerebrum
Central sulcus divides
Anterior frontal lobe from posterior parietal lobe
Lateral sulcus divides
Frontal and Parietal lobe from temporal lobe
Parieto-occipital sulcus divides
Parietal lobe from occipital lobe
The Cerebrum
Fig 14-12
The Cerebrum
Fig 14-12
The Cerebrum
Fig 14-12
The Cerebrum
Three Functional Principles of the Cerebrum
Each cerebral hemisphere receives sensory
information from, and sends motor commands to, the
opposite side of the body
The two hemispheres have different functions,
although their structures are alike
Correspondence between a specific function and a
specific region of cerebral cortex is not precise
The Cerebrum
White Matter of the Cerebrum
Association fibers
Commissural fibers
Projection fibers
The Cerebrum
White Matter of the Cerebrum Association fibers
Connections within one hemisphere:
– arcuate fibers: » are short fibers
» connect one gyrus to another
– longitudinal fasciculi: » are longer bundles
» connect frontal lobe to other lobes in same hemisphere
The Cerebrum
White Matter of the Cerebrum
Commissural fibers
Bands of fibers connecting two hemispheres:
– corpus callosum
– anterior commissure
The Cerebrum
White Matter of the Cerebrum
Projection fibers
Pass through diencephalon
Link cerebral cortex with:
– diencephalon, brain stem, cerebellum, and spinal cord
Internal capsule:
– all ascending and descending projection fibers
The Cerebrum
Fig 14-13
The Cerebrum
Fig 14-13
The Cerebrum
The Basal Nuclei
Also called cerebral nuclei
Are masses of gray matter
Are embedded in white matter of cerebrum
Direct subconscious activities
The Cerebrum
Structures of Basal Nuclei
Caudate nucleus
Curving, slender tail
Lentiform nucleus
Globus pallidus
Putamen
The Cerebrum
Fig 14-14
The Cerebrum
Fig 14-14
The Cerebrum
Fig 14-14
The Cerebrum
Functions of Basal Nuclei
Involved with
The subconscious control of skeletal muscle tone
The coordination of learned movement patterns
(walking, lifting)
Which of the following is NOT one of the basal nuclei?
A.Caudate nucleusB.Globus pallidusC.PutamenD.HippocampusE.Amygdaloid body
The Cerebrum
Motor and Sensory Areas of the Cortex Central sulcus separates motor and sensory
areas
Motor areas Precentral gyrus of frontal lobe:
– directs voluntary movements
Primary motor cortex:– is the surface of precentral gyrus
Pyramidal cells:– are neurons of primary motor cortex
The Cerebrum
Motor and Sensory Areas of the Cortex
Sensory areas
Postcentral gyrus of parietal lobe:
– receives somatic sensory information (touch, pressure,
pain, vibration, taste, and temperature)
Primary sensory cortex:
– surface of postcentral gyrus
The Cerebrum
Special Sensory Cortexes Visual cortex
Information from sight receptors
Auditory cortex Information from sound receptors
Olfactory cortex Information from odor receptors
Gustatory cortex Information from taste receptors
The Cerebrum
Fig 14-15
The Cerebrum
Association Areas
Cortical regions that interpret sensory information or
coordinate motor responses
Sensory association areas
Monitor and interpret arriving information at sensory areas of
cortex
Somatic motor association area (premotor cortex)
Coordinates motor responses (learned movements)
The Cerebrum
Sensory Association Areas
Somatic sensory association area
Interprets input to primary sensory cortex (e.g., recognizes
and responds to touch)
Visual association area
Interprets activity in visual cortex
Auditory association area
Monitors auditory cortex
The Cerebrum
Integrative Centers
Are located in lobes and cortical areas of both
cerebral hemispheres
Receive information from association areas
Direct complex motor or analytical activities
The Cerebrum
General Interpretive Area
Also called Wernicke area
Present in only one hemisphere
Receives information from all sensory association
areas
Coordinates access to complex visual and auditory
memories
The Cerebrum
Other Integrative Areas
Speech center Is associated with general interpretive area
Coordinates all vocalization functions
Prefrontal cortex of frontal lobe Integrates information from sensory association
areas
Performs abstract intellectual activities (e.g.,
predicting consequences of events or actions)
The Cerebrum
Fig 14-15
The Cerebrum
Interpretive Areas of Cortex
Brodmann areas
Patterns of cellular organization in cerebral cortex
Fig 14-15
The Cerebrum
Hemispheric Lateralization
Functional differences between left and right
hemispheres
Each cerebral hemisphere performs certain
functions that are not ordinarily performed by
the opposite hemisphere
The Cerebrum
The Left Hemisphere In most people, left brain (dominant hemisphere)
controls Reading, writing, and math
Decision making
Speech and language
The Right Hemisphere Right cerebral hemisphere relates to
Senses (touch, smell, sight, taste, feel)
Recognition (faces, voice inflections)
The Cerebrum
Fig 14-16
The Cerebrum
Monitoring Brain Activity
Brain activity is assessed by an
electroencephalogram (EEG)
Electrodes are placed on the skull
Patterns of electrical activity (brain waves) are
printed out
The Cerebrum
Four Categories of Brain Waves Alpha waves
Found in healthy, awake adults at rest with eyes closed Beta waves
Higher frequency Found in adults concentrating or mentally stressed
Theta waves Found in children Found in intensely frustrated adults May indicate brain disorder in adults
Delta waves During sleep Found in awake adults with brain damage
The Cerebrum
Fig 14-16
The Cerebrum
Synchronization A pacemaker mechanism
Synchronizes electrical activity between hemispheres
Brain damage can cause desynchronization
Seizure Is a temporary cerebral disorder Changes the electroencephalogram Symptoms depend on regions affected
The neural cortex is found on the surface of the _____.
A.cerebral hemispheresB.ponsC.cerebellumD.all of the aboveE.a and C only